1. Field of the Invention
The present invention relates generally to improved techniques for filtering and, more particularly, to a method for filtering undesired substances from dry cleaning fluids and an apparatus for accomplishing the same.
2. Background
Filtration is a much used technique for separating wanted substances from those which are unwanted. In one form of filtration, a filter separates the unwanted substances from a feed stream into a retentate which forms on the surface of the filter and a permeate which flows through the filter. In the dry cleaning industry, filtration systems are widely used for filtering dry cleaning solvents.
A serious issue facing society today is that of hazardous waste disposal. In the dry cleaning industry, the largest source of hazardous waste is from the filtration systems on dry cleaning machinery. Cartridge filtration systems are the most widely used systems for filtering dry cleaning solvents. A major disadvantage of these filtration systems is that they retain a relatively large amount of dry cleaning solvent within the cartridge. Since dry cleaning solvents such as pertchlorethylene are considered by regulators to be toxic, their presence within the used filters mandates their being treated as hazardous waste. With the increasing shortage of space in land fills forcing the cost of hazardous waste disposal up, the present use of cartridge filtration systems is becoming prohibitively expensive.
A currently available alternative to the cartridge filtration system is a modified flex tube or bag type powder type filter. The powder filter incorporates a series of finely woven polyester discs mounted on a hollow shaft. These discs are coated with a powder composed of diatomaceous earth which acts as the filtering material. These powder filters are regenerated by spinning the discs which throws all of the powder and the dirt off of the discs. The powder and dirt are then flushed to a still for cookdown. While this system does produce far less bulk and weight of hazardous waste than the cartridge filtration system, and is therefore less expensive to operate from a disposal point of view, this system does have the disadvantage of being quite labor intensive and time consuming.